Volatility, loss

Volatilization. The susceptibility of a herbicide to loss through volatilization has received much attention, due in part to the realization that herbicides in the vapor phase may be transported large distances from the point of application. Volatilization losses can be as high as 80—90% of the total applied herbicide within several days of application. The processes that control the amount of herbicide volatilized are the evaporation of the herbicide from the solution or soHd phase into the air, and dispersal and dilution of the resulting vapor into the atmosphere (250). These processes are influenced by many factors including herbicide application rate, wind velocity, temperature, soil moisture content, and the compound s sorption to soil organic and mineral surfaces. Properties of the herbicide that influence volatility include vapor pressure, water solubility, and chemical stmcture (251). 

Phenylcarbamates. Phenylcarbamate herbicides represent one of two subgroups of carbamate herbicides, the phenylcarbamates and the thiocarbamates (299). Both groups are prone to volatilization losses the thiocarbamates are particularly susceptible and should be sod-incorporated immediately after apphcation (2). The carbamate herbicides are used, in general, for the selective pre-emergence control of grass and broadleaved weeds (299). Exceptions would include barban, desmedipham, and phenmedipham which are appHed post-emergence. 

R. J. Keeling, "The Effect of Volatile Loss During Analysis on the Mechanical Spectra of PhenoHc/Kraft Composites," Conference Proceedings, Society... 

Fig. 2. Volatile loss of plasticizers from flexible PVC (BSS 35) where M represents Cg [...

Empirical evidence supporting the role of soil micro-layer losses in zero-time issues is given by the often-seen rise in post zero-time residue recoveries. The improved recoveries likely result from the micro-layer residue redistribution that reduces losses of the highly concentrated surface residues. There has been some speculation that zerotime core recoveries may be due to volatilization losses not measured by standard laboratory studies. If this were the case, however, increases in residue concentrations would not occur over time since volatilized residues would be lost to the atmosphere. ... 

Only one study specifically compared volatilization losses between organic and conventional soil. Ammonia volatilization is mainly caused by animal manure rather than by N fertilizers (Kirchmann et al. 1998). 

A small part of divalent mercury is reduced to mercury vapour. This reduction probably accounts for the ability of certain commonly occurring microorganisms to volatilize mercury for biological media [59]. Loss of volatile radioactive mercury was observed in rats injected with salts of divalent mercury labelled with the 203Hg isotope [60]. Part of the volatile mercury was exhaled via the lungs, the remainder by way of the skin and fur. The volatile loss accounted for up to 20% of the total rate of excretion of mercury from the animals. 

Alternatively 0.5g samples were dry ashed using magnesium nitrate as an ashing aid [168] to prevent volatilization losses of selenium. The solution was diluted to 50mL. Total selenium was determined by using 50pL aliquots diluted to 5mL with 0.5M hydrochloric acid. 

Volatilization loss can be a significant dissipation pathway for organics applied to land. The rate of dissipation of organics is governed by the vapour pressure of the compound, and on soil and environmental conditions. Losses to the atmosphere may take place immediately if the organics are applied at the soil surface if the organics are incorporated with the surface soil layer or injected below surface, the rate of volatilization loss is significantly reduced and is dependent on the rate of transport to the soil surface. As an example, 90% of Heptachlor applied on the soil surface may be lost in 2-7 days, in comparison to a 7% loss in 167 days when incorporated to 7.5cm [14]. 

Dorn et al. have studied the fate of epifenonane in polluted water (24). When Glatt River water was fortified with epifenonane at 10 ppm and exposed to open air for four weeks, 61% of the applied dose was recovered as intact epifenonane. Volatility losses amounted to 18% of the applied 3H while metabolites contributed a mere 21%. The characterized metabolites are listed in Table VI. The two major degradation routes involved epoxide modification and benzylic oxidation. 

Cenospheres are formed during heavy oil combustion. In the early stages of combustion, the oil particle is rapidly heated and evolves volatile species, which react in the gas phase. Toward the end of the volatile-loss phase, the generation of gas declines rapidly and the... 

Mikkelsen DS, De Datta SK, Obcemea WN. 1978. Ammonia volatilization losses from flooded rice soils. Soil Science Society of America Journal 42 725-730. 

Baur, J.R. andBovey, R.W. Ultraviolet and volatility loss of herbicides. Arch. Environ. Contam. Toxicol, 2(3) 275-288,1974. 

Volatilization losses should be insignificant since even the very volatile trifluralin was not lost. 

There Is also another pertinent question to be asked - what Is the relevance of these estimated H values, with their awkward units, to the natural environment One answer Is that comparisons of H values between different neutral organics can be helpful In a relative sense, particularly when one or more of the chemicals In the comparison have already been well characterized In the field. A second answer Is that H values can be used In calculations of volatilization from rivers (H ) and soil surfaces (91). Finally, to put H values In further perspective, the following soil volatilization data have been obtained from the literature (Table V). Clearly, the data are Inadequate to allow direct correlation between H and volatilization losses from soil. The data do show, however, that (1) even compounds with low H values can volatilize when applied to the surface, and (2) differences In application methods may significantly affect volatilization losses. 

K results mostly from volatile loss of this guest material. 

Sorbent Elution. The loaded extraction columns were disconnected and eluted with solvents individually. The elution procedure was as follows First, 1 column bed volume of pesticide-grade pentane was added to the sorbent to displace any residual water. Then, 3 column bed volumes of ethyl ether were added. The eluting solvents were collected in a 2-mL volumetric flask. The eluates from the primary and secondary columns were combined in the volumetric flask. The internal standard solution was added, and the final extract volume was adjusted to 2 mL. Air pressure was again used to push the solvents through the sorbents to avoid volatility losses. 

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